Q I have had my 1993 Fiat Tipo 1.4 ie since new and it has the Bosch Mono-Jetronic A2.4 injection system. I have tried to look after the machine so it will keep me in transport for as long as possible.
It has never let me down so far, but there is one glitch that is becoming more expensive as fuel prices rise: overfuelling at cold temperatures. Most of my journeys are 3-4 miles to town and back, so the fuel consumption in winter is twice that in warmer months.
I read an AA report that said that the fuel consumption on my Tipo prior to the engine warming up fully was higher than the previous model with a carburettor. When my engine is up to temperature, the fuel consumption is good whatever the outside temperature.
Can you tell me if the ECU on this vehicle can be remapped in any way to reduce the fuel consumption when cold? If the ECU could be tricked into thinking the temperature of the engine was higher, I would be able to cut my fuel consumption on short journeys in the winter. My previous vehicles could have the choke pushed in after two miles, but the electronic systems are linked to the coolant temperature. I have tried changing the thermostat but his has made no difference.
A First, I would advise changing the coolant temperature sensor. These do weaken with age and you may find that it is not giving the correct readings to the ECU. The sensor should give a reading of 5.97 kiloohms when cold and 0.24 kiloohms when the engine is at 90°.
The sensor works by varying the resistance – as it heats up, the resistance decreases. It is possible to cheat the system by connecting the two sensor wires together with a resistor between them. This would, in effect, lower the resistance, with the result that it tells the ECU the engine is warmer than it really is. A resistor of around 4 kiloohms should lower the resistance sufficiently to trick the ECU into thinking the engine is around 10-15° hotter than it is. Care will need to be taken as too low a resistance may end up damaging the ECU.
The problem with this is that if you lower the resistance by too much you may experience difficulty starting and the cooling fan may cut in too quickly. This should not be a problem on your Tipo as the radiator fan is operated by a separate switch.
Have A Problem Vehicle? Get In Touch…
If you have a problem vehicle, Car Mechanics has the answer in the shape of technical editor Steve Rothwell. Email your questions firstname.lastname@example.org.